C++ seekg,seekp,tellg,tellp

1.      seekg，tellg

Ø  功能：设置输入文件流的文件流指针位置

Ø  示例程序：

例1

// read a file into memory

#include <iostream>     // std::cout

#include <fstream>      // std::ifstream

 

int main () {

 std::ifstream is ("D:/test.txt", std::ifstream::binary);

  if (is) {

    // get length of file:

    is.seekg (0, is.end);//将读取is指针移到离is.end的0处意思是将此指针移到文件末尾

    int length = is.tellg();//返回输入流中的当前字符的位置。   is.seekg (0, is.beg);// 将读取is指针移到离is.beg的0处意思是将此指针移到文件开始

 

 

    // allocate memory:

char * buffer = new char [length+1];

memset(buffer,0,length+1);

 

    // read data as a block:

   is.read (buffer,length);

 

   is.close();

 

    // print content:

   std::cout.write (buffer,length);

 

    delete[] buffer;

  }

 

  return 0;

}

2.      seekp,tellp

Ø  功能：设置输出文件流的文件流指针位置

Ø  示例程序

例1

#include <fstream>      // std::ofstream

int main () {

  std::ofstream outfile;

  outfile.open ("D:/test.txt");

  outfile.write ("This is an apple",16);

  long pos = outfile.tellp();//返回当前文件指针的位置

  outfile.seekp (pos-7);

  outfile.write (" sam",4);

  outfile.close();

  return 0;

}